An organic solar cell is a device capable of directly converting solar energy to electric energy by applying a photovoltaic effect. Solar cells are divided into inorganic solar cells and organic solar cells depending on the materials forming a thin film. Typical solar cells are fabricated using a p-n junction by doping crystalline silicon (Si), an inorganic semiconductor. Electrons and holes generated by light absorption spread to p-n junction points, are accelerated by the electric field, and migrate to an electrode. Power conversion efficiency of this process is defined as a ratio of power given to an external circuit and solar power put into a solar cell, and the ratio has been accomplished up to 24% when measured under a currently standardized hypothetical solar irradiation condition. However, existing inorganic solar cells already has a limit in economic feasibility and material supplies, and therefore, organic material semiconductor solar cells that are readily processed, inexpensive and have various functions have been highly favored as a long-term alternative energy source.
For solar cells, it is important to increase efficiency so as to output as much electric energy as possible from solar energy. In order to improve efficiency of such solar cells, generating as much excitons as possible inside a semiconductor is important, however, taking the generated charges outside without loss is also important. One of the reasons for the charge loss is the dissipation of the generated electrons and holes by recombination. Various methods for delivering the generated electrons or holes to an electrode without loss have been proposed, however, most of the methods require additional processes, and accordingly, the fabricating costs may increase.